Bonsoir,
k(a + b) = ka + kb
(a + b)(c + d) = ac + ad + bc + bd
Développer:
A = 5(7a + 8)
A = 5*7a + 5*8
A = 35a + 40
B = 3a(9 - 3a)
B = 3a*9 + 3a*(-3a)
B = 27a - 9a²
B = -9a² + 27a
C = (4a - 7)(-2a + 5)
C = 4a*(-2a) + 4a*5 + (-7)*(-2a) + (-7)*5
C = -8a² + 20a + 14a - 35
C = -8a² + 34a - 35
* = multiplication
Bonne soirée.
